During 2009-2010, a large US mumps outbreak occurred affecting two-dose vaccinated 9th-12th grade Orthodox Jewish boys attending all-male yeshivas (private, traditional Jewish schools). Our objective was to understand mumps transmission dynamics in this well-vaccinated population. We surveyed 9th-12th grade male yeshivas in Brooklyn, NY with reported mumps case-students between 9/1/2009 and 3/30/2010. We assessed vaccination coverage, yeshiva environmental factors (duration of school day, density, mixing, duration of contact), and whether environmental factors were associated with increased mumps attack rates. Ten yeshivas comprising 1769 9th-12th grade students and 264 self-reported mumps cases were included. The average yeshiva attack rate was 14.5% (median: 13.5%, range: 1-31%), despite two-dose measles-mumps-rubella vaccine coverage between 90-100%. School duration was 9-15.5 h/day; students averaged 7 h face-to-face/day with 1-4 study partners. Average daily mean density was 6.6 students per 100 square feet. The number of hours spent face-to-face with a study partner and the number of partners per day showed significant positive associations (p < 0.05) with classroom mumps attack rates in univariate analysis, but these associations did not persist in multivariate analysis. This outbreak was characterized by environmental factors unique to the yeshiva setting (e.g., densely populated environment, prolonged face-to-face contact, mixing among infected students). However, these features were present in all included yeshivas, limiting our ability to discriminate differences. Nonetheless, mumps transmission requires close contact, and these environmental factors may have overwhelmed vaccine-mediated protection increasing the likelihood of vaccine failure among yeshiva students.
Keywords: environmental risk factors; high MMR vaccine coverage; mumps; mumps outbreak; mumps transmission.